/*
 * %W% %E%
 *
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang;

/**
 * A <tt>CharSequence</tt> is a readable sequence of <code>char</code> values.
 * This interface provides uniform, read-only access to many different kinds of
 * <code>char</code> sequences. A <code>char</code> value represents a character
 * in the <i>Basic Multilingual Plane (BMP)</i> or a surrogate. Refer to <a
 * href="Character.html#unicode">Unicode Character Representation</a> for
 * details.
 *
 * <p>
 * This interface does not refine the general contracts of the
 * {@link java.lang.Object#equals(java.lang.Object) equals} and
 * {@link java.lang.Object#hashCode() hashCode} methods. The result of comparing
 * two objects that implement <tt>CharSequence</tt> is therefore, in general,
 * undefined. Each object may be implemented by a different class, and there is
 * no guarantee that each class will be capable of testing its instances for
 * equality with those of the other. It is therefore inappropriate to use
 * arbitrary <tt>CharSequence</tt> instances as elements in a set or as keys in
 * a map.
 * </p>
 *
 * @author Mike McCloskey
 * @version %I% %E%
 * @since 1.4
 * @spec JSR-51
 */

//http://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/CharSequence.html
//http://docs.oracle.com/javase/6/docs/api/
//CharSequence 是 char 值的一个可读序列

/*
 *  char charAt(int index) 返回指定索引的 char 值。 
	int length() 返回此字符序列的长度。 
 	CharSequence subSequence(int start, int end)  返回一个新的 CharSequence，它是此序列的子序列。 
 	String toString()  返回一个包含此序列中字符的字符串，该字符串与此序列的顺序相同。 

 */

public interface CharSequence {

	/**
	 * Returns the length of this character sequence. The length is the number
	 * of 16-bit <code>char</code>s in the sequence.</p>
	 *
	 * @return the number of <code>char</code>s in this sequence
	 */
	int length();

	/**
	 * Returns the <code>char</code> value at the specified index. An index
	 * ranges from zero to <tt>length() - 1</tt>. The first <code>char</code>
	 * value of the sequence is at index zero, the next at index one, and so on,
	 * as for array indexing. </p>
	 *
	 * <p>
	 * If the <code>char</code> value specified by the index is a <a
	 * href="Character.html#unicode">surrogate</a>, the surrogate value is
	 * returned.
	 *
	 * @param index
	 *            the index of the <code>char</code> value to be returned
	 *
	 * @return the specified <code>char</code> value
	 *
	 * @throws IndexOutOfBoundsException
	 *             if the <tt>index</tt> argument is negative or not less than
	 *             <tt>length()</tt>
	 */
	char charAt(int index);

	/**
	 * Returns a new <code>CharSequence</code> that is a subsequence of this
	 * sequence. The subsequence starts with the <code>char</code> value at the
	 * specified index and ends with the <code>char</code> value at index
	 * <tt>end - 1</tt>. The length (in <code>char</code>s) of the returned
	 * sequence is <tt>end - start</tt>, so if <tt>start == end</tt> then an
	 * empty sequence is returned. </p>
	 * 
	 * @param start
	 *            the start index, inclusive
	 * @param end
	 *            the end index, exclusive
	 *
	 * @return the specified subsequence
	 *
	 * @throws IndexOutOfBoundsException
	 *             if <tt>start</tt> or <tt>end</tt> are negative, if
	 *             <tt>end</tt> is greater than <tt>length()</tt>, or if
	 *             <tt>start</tt> is greater than <tt>end</tt>
	 */
	CharSequence subSequence(int start, int end);

	/**
	 * Returns a string containing the characters in this sequence in the same
	 * order as this sequence. The length of the string will be the length of
	 * this sequence. </p>
	 *
	 * @return a string consisting of exactly this sequence of characters
	 */
	public String toString();

}
